For many years now, several powerful and effective insecticides have been used to protect food and fiber crops. More recently, there has been a great deal of controversy about the effect of these on the environment and some of the insecticides which have been in common use have been banned. Furthermore, other insecticides which are still in use are considered to be potentially harmful to the environment but are required to be used for lack of other alternatives.
As a result, a search has been going on for "biorational pesticides". These are compositions which would deter insects or other pests but would have no or minimal harmful effect on the environment.
One agent known to protect crops from pests is azadirachtin which is a natural product found in the seeds of the neem tree (Azadirachta indica A. Juss.). The neem tree is found in India, Pakistan, Bangladesh, Burma, Thailand, Malaysia and Africa, for example.
Azadirachtin has been extracted from neem seeds and found to have anti-feedant (deters insects from feeding on plants) and growth regulation potency against several pests including Japanese beetles, fall armyworms, locusts, termites, grasshoppers, tobacco hornworms, tobacco budworms, caterpillars, gypsy moths, rice weevils, aphids, cotton boll moths, and many others. It is readily applied by coating seeds or by applying a spray to the crops themselves. See for example J. Environ. Sci. Health, A17 (1), 57-65 (1982) by J. B. Stokes and R. E. Redfern of the USDA.
While azadirachtin is a known agent, it has not come into commercial use because it has stability problems. For example, its instability in sunlight has been known and is the subject of the aforementioned article by Stokes and Redfern. That article indicates that sunlight degradation is hindered by leaving some neem oil in with the azadirachtin or by adding other plant oil and that further aid is given by including a sunscreen (a uv-absorbing additive). Azadirachtin has also been found to have storage stability problems whereby it deactivates in the container or after application simply on the passage of time. No solution has been suggested in the published literature for these problems.